1. Field of the Invention
The present invention relates to a cutting plotter for consecutively cutting a cutting sheet in accordance with image data produced by a computer so as to make desired mortised images, and in particular to a cutting plotter using a roll type cutting sheet as a cutting sheet.
2. Description of the Related Art
The representative cutting plotters of this type are disclosed in, for example, U.S. Pat. No. 4,996,651, U.S. Pat. No. 5,188,009 or U.S. Pat. No. 5,443,194. In particular, a device disclosed in U.S. Pat. No. 5,443,194 uses a rolled cutting sheet as a cutting sheet. The cutting plotter of this type is used for making dress fitting patterns or signing labels to be pasted onto show-windows for enhancing advertising effects. Such a cutting plotter successively receives image data to be cut out (borderline data of the image, hereinafter referred to as "cutting data") from a computer such as a CAD device, and obtains desired mortised images by moving a cutting pen in succession following a sequence of cutting data.
In a device using a rectangular cutting sheet as disclosed in U.S. Pat. No. 4,996,651, mortised images are limited to sizes smaller than the size of the instant cutting sheet. However, in the case of using the roll type cutting sheet as in the device of U.S. Pat. No. 5,443,194, the continuous cutting sheet can be drawn out in succession by feeding the cutting sheet in a y direction. Such a mortised image of considerably large size in the y direction can be also produced.
The image lengthy in the feeding direction of the rolled cutting sheet, i.e., in the y direction is cut out by the cutting pen while the rolled cutting sheet is fed in the y direction. However, the cutting may confront an abrupt increase in feeding resistance of the cutting sheet during cutting. This is caused by existences of a firmly rolled part and an already fed part drawn from the firmly rolled part in the cutting sheet on use in the device of this type. This is because cutting of a portion exceeding the already fed amount requires superfluous force for loosening the rolling of the rolled part although the cutting is normally carried out for the already drawn cutting sheet.
When such a case occurs, a new cutting is made different from the cutting action up to that time and the cutting part is disordered (sharpness at a cut end is soft), or a cutting line traces a different locus from the desired line, so that cut qualities are very deteriorated and the cutting speed is remarkably delayed.